text: from contextlib import contextmanager
  
  from glue.core.message import (DataCollectionAddMessage,
                                 DataCollectionDeleteMessage,
                                 ComponentsChangedMessage)
  from glue.core.registry import Registry
  from glue.core.link_manager import LinkManager
  from glue.core.data import Data, BaseCartesianData
  from glue.core.hub import Hub, HubListener
  from glue.core.coordinates import WCSCoordinates
  from glue.config import settings, data_translator
  from glue.utils import as_list, common_prefix
  
  
  __all__ = ['DataCollection']
  
  
  class DataCollection(HubListener):
  
      """The top-level object for interacting with datasets in Glue.
  
      DataCollections have the following responsibilities:
  
         * Providing a way to retrieve and store data
         * Broadcasting messages when data are added or removed
         * Keeping each managed data set's list of
           :class:`~glue.core.component.DerivedComponent` instances up-to-date
         * Creating the hub that all other objects should use to communicate
           with one another (stored in ``self.hub``)
      """
  
      def __init__(self, data=None):
          """
          :param data: :class:`~glue.core.data.Data` object, or list of such objects
          """
          super(DataCollection, self).__init__()
  
          self._link_manager = LinkManager(self)
          self._data = []
  
          self.hub = None
  
          self._subset_groups = []
          self.register_to_hub(Hub())
          self.extend(as_list(data or []))
          self._sg_count = 0
  
          self._link_manager.register_to_hub(self.hub)
  
      @property
      def data(self):
          """ The :class:`~glue.core.data.Data` objects in the collection """
          return self._data
  
      def append(self, data):
          """ Add a new dataset to this collection.
  
          Appending emits a DataCollectionAddMessage.
          It also updates the list of DerivedComponents that each
          data set can work with.
  
          :param data: :class:`~glue.core.data.BaseCartesianData` object to add
          """
  
          if isinstance(data, list):
              self.extend(data)
              return
  
          if data in self:
              return
  
          if not isinstance(data, BaseCartesianData):
              raise TypeError("Only BaseCartesianData subclasses can be used at this time")
  
          self._data.append(data)
  
          if self.hub:
              data.register_to_hub(self.hub)
              for s in data.subsets:
                  s.register()
              msg = DataCollectionAddMessage(self, data)
              self.hub.broadcast(msg)
  
          self._sync_link_manager()
  
      def extend(self, data):
          """Add several new datasets to this collection
  
          See :meth:`append` for more information
  
          :param data: List of data objects to add
          """
          # Wait until all datasets are added to sync the link manager
          with self._no_sync_link_manager():
              for d in data:
                  self.append(d)
          self._sync_link_manager()
  
      def remove(self, data):
          """ Remove a data set from the collection
  
          Emits a DataCollectionDeleteMessage
  
          :param data: the object to remove
          :type data: :class:`~glue.core.data.Data`
          """
          if data not in self._data:
              return
          self._data.remove(data)
          Registry().unregister(data, Data)
          if self.hub:
              msg = DataCollectionDeleteMessage(self, data)
              self.hub.broadcast(msg)
  
      def clear(self):
          with self._no_sync_link_manager():
              for data in list(self):
                  self.remove(data)
  
      def _sync_link_manager(self):
          """ update the LinkManager, so all the DerivedComponents
          for each data set are up-to-date
          """
  
          if getattr(self, '_disable_sync_link_manager', False):
              return
  
          # Avoid circular calls
          with self._no_sync_link_manager():
              self._link_manager.update_externally_derivable_components()
  
      @contextmanager
      def _no_sync_link_manager(self):
          self._disable_sync_link_manager = True
          yield
          self._disable_sync_link_manager = False
  
      @property
      def links(self):
          """
          Tuple of :class:`~glue.core.component_link.ComponentLink` objects.
          """
          return tuple(self._link_manager.links)
  
      @property
      def external_links(self):
          """
          Tuple of :class:`~glue.core.component_link.ComponentLink` objects.
          """
          return tuple(self._link_manager.external_links)
  
      def add_link(self, links):
          """Add one or more links to the data collection.
  
          This will auto-update the components in each data set
  
          :param links:
             The links to add. A scalar or list of
             :class:`~glue.core.component_link.ComponentLink`
             instances, or a :class:`~glue.core.link_helpers.LinkCollection`
          """
          self._link_manager.add_link(links)
  
      def remove_link(self, links):
          """
          Remove one or more links from the data collection.
  
          This will auto-update the components in each data set
  
          :param links:
             The links to remove. A scalar or list of
             :class:`~glue.core.component_link.ComponentLink`
             instances, or a :class:`~glue.core.link_helpers.LinkCollection`
          """
          self._link_manager.remove_link(links)
  
      def _merge_link(self, link):
          pass
  
      def set_links(self, links):
          """
          Override the links in the collection, and update data objects as
          necessary.
  
          :param links: The new links. An iterable of
              :class:`~glue.core.component_link.ComponentLink` instances
          """
          self._link_manager.clear_links()
          self._link_manager.add_link(links)
  
      def register_to_hub(self, hub):
          """ Register managed data objects to a hub.
  
          :param hub: The hub to register with
          :type hub: :class:`~glue.core.hub.Hub`
          """
          if self.hub is hub:
              return
          if self.hub is not None:
              raise RuntimeError("Data Collection already registered "
                                 "to a different Hub")
  
          if not isinstance(hub, Hub):
              raise TypeError("Input is not a Hub object: %s" % type(hub))
          self.hub = hub
  
          # re-assign all data, subset hub instances to this hub
          for d in self._data:
              d.register_to_hub(hub)
              for s in d.subsets:
                  s.register()
  
          hub.subscribe(self, ComponentsChangedMessage,
                        lambda msg: self._sync_link_manager(),
                        filter=lambda x: x.sender in self._data)
  
      def new_subset_group(self, label=None, subset_state=None):
          """
          Create and return a new Subset Group.
  
          :param label: The label to assign to the group
          :type label: str
          :param subset_state: The state to initialize the group with
          :type subset_state: :class:`~glue.core.subset.SubsetState`
  
          :returns: A new :class:`~glue.core.subset_group.SubsetGroup`
          """
          from glue.core.subset_group import SubsetGroup
          color = settings.SUBSET_COLORS[self._sg_count % len(settings.SUBSET_COLORS)]
          self._sg_count += 1
          label = label or 'Subset %i' % self._sg_count
  
          result = SubsetGroup(color=color, label=label, subset_state=subset_state)
          self._subset_groups.append(result)
          result.register(self)
          return result
  
      def remove_subset_group(self, subset_grp):
          """
          Remove an existing :class:`~glue.core.subset_group.SubsetGroup`
          """
          if subset_grp not in self._subset_groups:
              return
  
          # remove from list first, so that group appears deleted
          # by the time the first SubsetDelete message is broadcast
          self._subset_groups.remove(subset_grp)
          for s in subset_grp.subsets:
              s.delete()
          subset_grp.unregister(self.hub)
  
      def suggest_merge_label(self, *data):
          """
          Determine what merge label to suggest given datasets
          """
  
          # Find longest common prefix for data
          suggestion = common_prefix([d.label for d in data])
  
          if len(suggestion) < 3:
              suggestion = 'Merged data'
  
          # Now check if the suggestion already exists, and if so add a suffix
          labels = self.labels
          if suggestion in labels:
              suffix = 2
              while "{0} [{1}]".format(suggestion, suffix) in labels:
                  suffix += 1
              suggestion = "{0} [{1}]".format(suggestion, suffix)
  
          return suggestion
  
      @property
      def labels(self):
          return [d.label for d in self]
  
      def merge(self, *data, **kwargs):
          """
          Merge two or more datasets into a single dataset.
  
          This has the following effects:
  
          All components from all datasets are added to the first argument
          All datasets except the first argument are removed from the collection
          Any component name conflicts are disambiguated
          The pixel and world components apart from the first argument are discarded
  
          :note: All arguments must have the same shape
  
          :param data: One or more :class:`~glue.core.data.Data` instances.
          :returns: self
          """
          if len(data) < 2:
              raise ValueError("merge requires 2 or more arguments")
          shp = data[0].shape
          for d in data:
              if d.shape != shp:
                  raise ValueError("All arguments must have the same shape")
  
          label = kwargs.get('label', data[0].label)
  
          master = Data(label=label)
          self.append(master)
  
          master.coords = data[0].coords
          for i, d in enumerate(data):
              if isinstance(d.coords, WCSCoordinates):
                  master.coords = d.coords
                  break
  
          # Find ambiguous components (ones which have labels in more than one
          # dataset
  
          from collections import Counter
          clabel_count = Counter([c.label for d in data for c in d.main_components + d.derived_components])
  
          for d in data:
  
              for c in d.components:
  
                  if c in master.components:  # already present (via a link)
                      continue
  
                  # Don't include coordinate components here as they will be
                  # recomputed separately once the first non-coordinate component
                  # is added.
                  if c in d.coordinate_components:
                      continue
  
                  lbl = c.label
  
                  if clabel_count[lbl] > 1:
                      lbl = lbl + " [{0}]".format(d.label)
  
                  c._label = lbl
                  c.parent = master
                  master.add_component(d.get_component(c), c)
  
              self.remove(d)
  
          return master
  
      @property
      def subset_groups(self):
          """
          tuple of current :class:`Subset Groups <glue.core.subset_group.SubsetGroup>`
          """
          return tuple(self._subset_groups)
  
      def __contains__(self, obj):
          return (obj in self._data or
                      obj in self.subset_groups or
                      any([data.label == obj for data in self._data]))
  
      def __getitem__(self, key):
          if isinstance(key, str):
              matches = [data for data in self._data if data.label == key]
              if len(matches) == 0:
                  raise ValueError("No data found with the label '{0}'".format(key))
              elif len(matches) > 1:
                  raise ValueError("Several datasets were found with the label '{0}'".format(key))
              else:
                  return matches[0]
          else:
              return self._data[key]
  
      def __setitem__(self, key, data):
          """
          Add a dataset to the data collection.
  
          This can be either a :class:`~glue.core.data.Data` object, which will
          then have its label set to the specified key, or another kind of
          object which will be automatically translated into a
          :class:`~glue.core.data.Data` object.
          """
  
          if not isinstance(key, str):
              raise TypeError("item key should be a string, but got {0}".format(type(key)))
  
          if not isinstance(data, Data):
  
              handler, preferred = data_translator.get_handler_for(data)
  
              data = handler.to_data(data)
              data._preferred_translation = preferred
  
          data.label = key
  
          for existing_data in self._data[:]:
              if existing_data.label == key:
                  self.remove(existing_data)
  
          self.append(data)
  
      def __iter__(self):
          return iter(self._data)
  
      def __len__(self):
          return len(self._data)
  
      def index(self, item):
          return self._data.index(item)
  
      def __str__(self):
          if len(self) == 1:
              result = "DataCollection (1 data set)\n\t"
          else:
              result = "DataCollection (%i data sets)\n\t" % len(self)
  
          result += '\n\t'.join("%3i: %s" % (i, d.label) for
                                i, d in enumerate(self))
          return result
  
      def __repr__(self):
          return self.__str__()
  
      def __bool__(self):
          return True
  
      def __nonzero__(self):
          return True
  